Treatment of magnesium-base alloys



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Patented May 14, 1929.

UNITED STATES-PATENT OFFICE.

JOHN A. GANN, OF MIDLAND, MICHIGAN, AE 'GNOR TO THE DOW CHEMICAL COM-IPANY, 0F MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN.

TREATMENT OF MAGNESIUM-BASE ALLO YS.

No Drawing.

In my co-pending application filed November 28, 1921, Ser. No. 518,142,I describe an improvement in the art of making alloy articles havingmagnesium as the prmcipal ingredient and containing one or more metalscapable of dissolving in solid magnesium in larger amounts than arefound in solution in the alloy as cast, such improvement consisting insubjecting such an article. to a heat treatment at high temperature butbelow the melting temperature of the most fusible constituent of thealloy. The result of the aforesaid treatment is to cause increasedsolution of the other metal or metals in the solid magnesium, this beingaccompanied by a marked increase in the strength and/or plasticity ofthe article as well as in the im rovement thereof in other of itsphysica characteristics. The increase in plasticity thus obtained inlight metal alloy articles of the class in question is of particularimportance Where it is desired subsequently to subject the article toplastic deformation, such for example as a forging, drawing, rolling orextrudin operation. The articles thus treated are a so found to berendered susceptible to further improvement in certain physicalqualities by aging at regulated temperatures.

The improvements herein claimed relate to certain specific aspects ofthe process and resultant product described in my aforesaid application,it being noted that other such specific aspects are separately presentedin my co-pending application filed January 13, 1927, Ser. No. 161,029. 1It has been found, in other words, that specifically different resultsmay be obtained, depending upon the constitution of the alloy that issubjected to the aforesaid heat treatment, and while a wider field ofuse will probably be found with magnesiumaluminum alloys, other binaryas well as ternary and more complex magnesium alloys are susceptible tomarked improvement by treatment in the fashion described.

in the claims, the following description setting forth but one of thevarious ways in Application filed March 29, 1927. Serial IllTo. 179,402,

principle of the invention may is placed on the improved resultsobtained by my method of regulated heat treatment in the case of amagnesium-aluminum alloy, the one selected by way of example contain ingfrom 6 to 8 per cent aluminum. However, reference is also made in saidapplication, as well as in my second co-pending application, to theeffect of such heat treatment on a ternary or more complex magnesiumalloy, in which at least part of the added metals form eutectics withthe magnesium and said eutectics have different melting points and varyas to the ease with which they dissolve in the magnesium to form solidsolutions whereby one or more of the added metals are caused to bepresent both as solid solution and eutectic, while the other or othersare present either as solid solution or eutectic. As an example of thelatter, magnesium-aluminum-zinc-copper-cadmium alloys are cited in whichthe eat treatment may be such that aluminum and zinc are present as bothsolid solutions and eutectic, while the copper is present as eutecticand the cadmium is completely in solid solution.

A typical alloy of the kind in question is one containing approximately8.5 per cent of aluminum, 2 per cent of copper and l per cent of zinc,with or without a corresponding small percentage of cadmium, the balancebeing magnesium. Such an alloy as cast will contain an eutecticstructure formed by each of the three first-named alloying ingredientswith the magnesium, in

addition to a certain amount of solid solu-' tion formed by the aluminumand zinc with the magnesium. The copper, on the contrary, will not formsuch solid solution and this remains true even after heat treatment ofthe alloy, while, on the contrary, all of the cadmiumimmediately goesinto such solution and so remains.

The melting point of the Mg-Al eutectic is 824 degrees F., while theMg-Zn eutectic melts at 650 degrees F. Accordingly, in carrying out mymethod of regulated heat treatment in' the case of such an alloy, it

heat treatment may be stopped short of the point of such completesolution of the aluminum so as to leave a residual Mg-Al eutecticstructure. In any event the alloy after heat treatment will retain, asabove oxplaiued, the Mg-Cu eutectic structure which does not dissolve at.all, although the p1' e scribed heat treatment may cause somerearrangement of this eutectic with attendant relief of casting strainsthat may be present in the article. Similarly, where cadmium is present,such heat treatment will insure a more uniform distribution thereof insolution by eliminating cored crystals which otherwise may be present.

It will be understood, of course, that a lower temperature may beemployed in each of the foregoing stagcs of the heat treatment, providedthe latter be suiliciently prolonged. The change in the micro-structureof the alloy serves very definitely to establish the completion of theheat treatment, whether conducted at a lower temperature for such longerperiod or at a higher tcmperature approximating the maximum permissibletemperature as determined by themelting point of the more fusibleeutectic present in the alloy.

The term eutectic, as herein, used, it will be understood, includes not'only the well-known ordinary, eutectics with their more or lesscharacteristic. lamellar or globular structure, but also individual moreor less well-defined metallic or intermetallic crystals which so oftenoccur with relatively small percentages of added constituents.

Other modes of applying the principle of my invention may be employedinstead of the one explained, change being made as regards thecomposition and method herein disclosed, provided the ingredients orsteps stated by any of the following claims or the equivalent of suchstated ingredients or steps be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In the art of making light metal alloy articles wherein magnesium isthe predominant constituent, the alloy containing as minor constituentstwo other metals capable of forming eutectics differing as to theirmelting points, and also as to ease with which they dissolve in themagnesium to form a solid solution, the steps which consist in heatingsuch an article at a high temi to form a solid solution, the steps whichconsist in heating such an article at a high temperature but below themelting point of the more fusible eutectic, to cause substantiallycomplete solution of the same, and thou heating such article at a highertemperature but below the melting point of the less fusible eutectic tocause substantially complete solution thereof.

3. In the art of making light metal alloy articles wherein magnesium isthe predominant constituent, the alloy containing as minor constituentstwo other metals capable of forming eutectics differing as to theirmelting points, and also as to case with which they dissolve in themagnesium to form a solid solution, said alloy also containing as aminor constituent a metal forming a substantially insoluble eutecticwith the magnesium, the steps which consist in heating such an articleat a high temperature but below the melting point of the more fusible ofsuch soluble eutectics, to cause substantially complete solutionthereof, and then heating such article at a higher temerature but belowthe melting point of the ess fusible of such soluble eutectics to causeincreased solution thereof.

4. In the art of making light metal alloy articles wherein magnesium isthe predominant constituent, the alloy containing as minor constituentstwo other metals capable of forming eutectics diil'cring as to theirmelting points, and also as to ease with which they dissolve in themagnesium to form a solid solution, said alloy also containing as aminor constituent a metal forming a substantially insoluble eutecticwith the magnesium, the steps which consist in heating such an articleat a high temperature but below the melting point of the more fusible ofsuch soluble eutectics, to cause substantially complete solutionthereof, and then heating such article at a higher tomperaturo but belowthe melting point of the less fusible of such soluble eutectics to causesubstantially complete solution thereof.

5. In the art of making light metal alloy nant constituent, the

heating such article at the step which consists in heating such anarticle at a high temperature, but below the melting point of theeutectic formed by the zinc to cause substantially complete solutionthereof. a

6. In the art of making light metal alloy articles wherein magnesium isthe pre dominant constituent, the alloy containing zinc and aluminum asminor constituents, the step which consists in heating such an articleat a high temperature, but below the melting point of the eutecticformed by the zinc to cause substantially complete solution thereof, andthen heating such article at a higher temperature but below the meltingpoint of the eutectic formed by the aluminum to cause increased solutionthereof.

7. In the art of making light metal alloy articles wherein magnesium isthe predominant constituent, the alloy containing zinc and aluminum asminor constituents,

the step which consists in heating such an b article at a hightemperature, but below the melting point of the eutectic formed by thezinc to cause substantially complete solution thereof, and then heatingsuch article at a higher temperature but below the melting point of theeutectic formed by the aluminum to cause substantially complete solutionthereof.

8. In the art of making light metal alloy articles wherein magnesium isthe predominant constituent, the alloy containing zinc, aluminum andcopper as minor constituents, the step which consists in treating suchan article at a high temperature, but below the melting point of theeutectic formed by the zinc, to cause substantially complete solution ofthe latter.

9. ln the art of making light metal alloy articles wherein magnesium isthe predomialloy containing zinc, aluminum and copper as minorconstituents, the step which consists in treating such an article at ahigh temperature, but below the melting point of the eutectic formed bythe zinc, to cause substantially complete solution of the latter, andthen heating such article at a higher temperature but below the meltingpoint of the eutectic formed by the aifuminum to cause increasedsolution there- 0 l0. lln the art of making light metal alloy articleswherein magnesium is the predominant constituent, the alloy containingzinc, aluminum and copper as minor constituents, the step which consistsin treating such an article at a high temperature, but below the meltingpoint of the eutectic formed by the zinc, to cause substantiallycomplete solution of the latter, and then a higher temperature but belowthe melting point of the eutectic formed by the aluminum to causesubstantially complete solution thereof.

11. As an article of manufacture, a heat treated light metal alloyarticle, wherein magnesium is the predominant constituent, the alloyalso containing as minor constituents two other metals capable offorming eutectics differing as to their melting points as also as to thecase with which they dissolve in the magnesium to form a solid solution, such treated article being characterized by having a. greateramount of the more soluble constituent present in-solution than in anuntreated article of the same composition.

12. As an article of manufacture, a heat treated light metal alloyarticle, wherein magnesium is the predominant constituent, the alloyalso containing as minor constituents two other metals capable offorming eutectics difi'ering as totheir melting points as also as to theease with which they dissolve in the magnesium to form a solid solution,such treated article being characterized y having substantially all ofthe more soluble constituent present in solution.

13. As an article of manufacture, a heat I treated light metal alloyarticle, wherein magnesium is the predominant constituent, the alloyalso containing as minor constituents two other metals capable offorming eutectics differing as to their melting points as also as to theease with which they dissolve in the magnesium to form a solid solution,such treated article being characterized by having substantially all ofboth such minor constituents present in solution.

14. As an article of manufacture, a heat treated light metal alloyarticle, wherein magnesium is the predominant constituent, the alloyalso containing zinc and aluminum as minor constituents, such treatedarticle being characterized by having a greater amount of zinc presentin solution than in an untreated article of the same composi- ,tion.

15. As an article of manufacture, a heat treated light metal alloyarticle, wherein magnesium is the predominant constituent,

the alloy also containing zinc and aluminum as minor constituents, suchtreated article being characterized by having all of the zinc present insolution.

16. As anarticle of manufacture,a heat treated light metal alloyarticle, wherein magnesiun'1 is thepredominant constituent,

ing all of the zinc present in solution, the copper remaining in theeutectic structure.

18. As an article of manufacture, a heat treated light metal alloyarticle, wherein magnesium is the predominant constituent, the alloyalso containing zinc, aluminum and copper as minor constituents, suchtreated article being characterized by having a greater amount of zincand aluminum present in solution than in an untreated article of thesame composition, the copper remaining in the eutectic structure.

19. As an article of manufacture, a heat treated light metal alloyarticle, wherein magnesium is the predominant constituent, the alloyalso containing zine, aluminum and copper as minor constituents, suchtreated article being characterized by having substantially all of thezinc and aluminum present in solution, the copper remaining in aeutectic structure.

Signed by me this 19th day of January,

JOHN A. GANN.

